Converters are utilized in a variety of applications, such as for high speed motor and industrial machine drive applications and for energy generation and storage applications. For example, many hybrid or electric vehicles include an electric traction drive system that includes a 3-phase permanent magnet alternating current (AC) electric machine that is driven by a converter. The converter is supplied with power from a direct current (DC) power source, such as a storage battery, or from an AC power source, such as a wind turbine, wherein AC power is transformed into DC power by an AC to DC power converter or rectifier. Windings of a 3-phase AC electric machine can be coupled to converter legs (phase legs) of the power converter, wherein each converter leg includes a number of switches. Each switch is controlled by an associated gate drive unit which, based upon control signals from a central controller, generates ON/OFF switching signals that are provided to the corresponding switch. The switching signals applied to the converter legs of the converter cause the switches of the converter legs to switch on and off in an appropriate manner to convert the DC power to AC power. This AC power drives the AC electric machine, which in turn drives a shaft of the hybrid or electric vehicle drive train. Similar applies if AC power is to be converted into DC power by a converter, such as for use in high voltage direct current (HVDC) applications, for example.
In some high speed motor applications, such as for uninterruptible power supply using flywheel generators, for example, high speed induction motors are driven by an AC to AC power converter with a speed of more than 6,000 rpm. There are high speed drive systems which are capable of directly driving turbo-compressors at speeds of up to 20,000 rpm. In such high speed motor drive systems the motor fundamental frequency can vary from 100 Hz to 300 Hz, which requires high operating frequencies in the range of several hundred Hz or several kHz.
In the past gate drive units used in power converters were analog power amplifiers that excepted a low-power input from a central controller and produced a high-current drive input for the gate of a high-power transistor, such as an insulated gate bipolar transistor (IGBT) or a power metal-oxide-semiconductor field-effect transistor (MOSFET), used in a power converter. Recently, digital gate drive units have been developed for use in power converters. For example, U.S. Pat. No. 8,923,365 B2 discloses a digital gate drive unit for a power converter comprising a programmable logic controller (PLC) or a field programmable gate array (FPGA) and further including a DC power supply, a command link connector, a memory, and several signal connections. The gate drive unit is connected with a central controller via a command link to receive command signals from the central controller. In response to the command signals, the gate drive unit may select one of a plurality of pre-determined values or set points for the gate drive voltage that are stored in a lookup table within the memory and adjust the output stage to match the driving strength to the set point. The central controller and the gate drive unit communicate with each other via the command link such that the central controller may provide configuration and operational data to the gate drive unit on the same link as used for the ON/OFF command signals via modulation of the command signal and the gate drive unit may return feedback information, such as measured sensor values, to the central controller. The transmission of reconfiguration data permits in-operation re-programming of the gate drive unit as a field change or the like. Each gate drive unit transmits its serial number and the serial number of the corresponding semiconductor power switch to permit the central controller to authenticate the power converter components, so as to issue a reliable response to the command signal by the power converter. The feedback information allows the central controller to calculate and send configuration data for setting the gate drive unit to provide appropriate gate drive voltage to the corresponding power switch. With the newly introduced digital gate drive units and the communication of the gate drive unit with the controller it is possible to adapt the operational parameter to increase converter efficiency and to achieve a high accuracy of the voltages generated by the power converter.
Such high operational efficiencies and accuracies make the power converter also suitable for use in sophisticated high speed military and nuclear applications like for military aviation, military submarines or centrifuges for uranium enrichment. Such military and nuclear applications require high efficient, accurate and reliable converters which can provide exact high frequency voltages with a voltage and frequency stability within a prescribed tolerance. Modern high frequency converters and high speed drives utilizing same are able to meet such highly demanding requirements.
One issue with the modern technology of power converters is the risk for dual use of parts of the power converters such that a converter that was originally developed for civilian applications might be misused in a military application. For example, power converters intended for civilian applications might be disassembled into pieces and be assembled with other parts and reconfigured for use in military or nuclear weapon applications. It is desired to protect power converters against such a tampering and overbuilding.
In order to prevent dual use or misuse of high technology originally developed for civilian applications in military or nuclear applications, many countries impose export restrictions on such high technology products and equipment which meet or exceed certain performance characteristics. For example, in connection with frequency changers, converters or inverters which can easily be removed or used for other purposes, including military and nuclear purposes, U.S. export control regulations are very restrictive in defining that any power converter and the like, where the hardware can achieve an output frequency higher than 599 Hz with a frequency stability better than 0.2% will require an export license. Similar regulations also exist in the European Union and in other countries throughout the world. Obtaining an export license might be problematic, time consuming and costly. It is desired to achieve that higher frequency converters that can be used in civilian applications do not fall under the export control restrictions.